During the last 20 years, ecological research on
landscape fragmentation due to transportation infrastructure and urban
development has revealed a huge number of adverse effects, in
particular on animal populations. Today, it is known as a major reason
for the endangerment of animal populations and the extinction of
species in many industrialized regions of Central Europe as well as in
other industrialized parts of the world.

Since 1985, several political declarations of the German
Government and its advisory committees have demanded a turnaround in
the progressive degradation of the landscapes in Germany. However, the
trend of increasing landscape fragmentation has continued. This calls
for more efficient policies.

The issue of landscape fragmentation includes ecological
processes, perceptions of the effects by society, economic land-use
interests, and ethical principles. The interconnections between these
aspects leads to a transdisciplinary research question:

"How can
structural landscape alterations and their
effects be evaluated with regard to ethical principles and the values
of the persons concerned by the effects (or involved in the
decision-making process)? What are the conditions for acting
responsibly in the decision-making process?"

Landscape fragmentation is a growing problem. In order to
find solutions, the following six questions have to be addressed (among
others):

What is
"landscape fragmentation", and by which criteria and metrics can the
degree of fragmentation be characterized and quantitatively measured?

By which
criteria can the impact of fragmenting intrusions and of different
fragmenting patterns be assessed?

Which
mitigation measures are most effective in reducing the harmful
consequences of traffic and urban areas?

Which
conditions have to be met so that decision-makers can take
responsibility for landscape-fragmenting intrusions and their effects?

What
consequences do the extreme complexity of ecological interactions and
the difficulties in predicting ecological effects have for choosing a
proper evaluation concept?

How can
verifiable objectives for the future dimension of landscape
fragmentation be developed and achieved?

The patterns of perception and valuation held by the
participants of the decision-making process, e.g., experts from traffic
planning, nature protection, and landscape planning, can be
investigated by qualitative expert interviews. It is the reality of the
decision makers' perspectives and judgements that determines the
decisions on future landscape intrusions.

Our knowledge about the effects, however, is still
limited and, therefore, has little predictive power. Dealing with these
limitations is an unsolved problem. Very often, there is a "circle of
immunization". It stabilizes the process of increasing landscape
fragmentation by leaving uncertainties that cannot be handled routinely
in the environmental compatibility studies—such as effects on genetic
exchange or cumulative effects—out of consideration. Therefore, these
uncertainties do not have a retarding effect on the process of
landscape fragmentation. In addition, there is no commitment for
subsequently discovered ecological damages such as the loss of a
species as an effect of road construction.

As an answer to ecological overcomplexity (and
the resulting "Tantalus problems"), the concept of
environmental threat proposes to refer to appropriate
characteristics of the intrusions themselves—as indicators of their
potential harmfulness like, for example, persistence and spatial
range of environmental chemicals—instead of the poorly predictable
effects.

Suitable criteria for assessing landscape intrusions can
be geometric-structural or functional such as the degree of
landscape fragmentation and the
reduction of landscape connectivity. 'Landscape connectivity' is
defined as the degree to which landscape structure facilitates or
impedes the movement of animals. For example, the quantitative
landscape metric 'effective mesh size', meff, can be
applied for balancing new
landscape-dissecting intrusions and the removal of existing
barriers—particularly in environmental compatibility studies on the
level of regional planning. Furthermore, it seems to be useful for
providing landscape objectives (environmental quality goals) and the
development of limiting standards to curtail landscape fragmentation as
a contribution to the turnaround which has been called for in political
declarations.